docs: def open(self):
          """Open the files
          """
          segments = []
  
          files = config.get('env', 'jpl', fallback=[])
  
          if not files:
              raise JplConfigError("No JPL file defined")
  
          # Extraction of segments from each .bsp file
          for filepath in files:
  
              filepath = Path(filepath)
  
              if filepath.suffix.lower() != ".bsp":
                  continue
  
              segments.extend(SPK.open(str(filepath)).segments)
  
          if not segments:
              raise JplError("No segment loaded")
  
          # list of available segments
          self.segments = dict(((s.center, s.target), s) for s in segments)
  
          # This variable will contain the Target of reference from which
          # all relations between frames are linked
          targets = {}
  
          for center_id, target_id in self.segments.keys():
  
              center_name = target_names.get(center_id, 'Unknown')
              target_name = target_names.get(target_id, 'Unknown')
  
              # Retrieval of the Target object representing the center if it exists
              # or creation of said object if it doesn't.
              center = targets.setdefault(center_id, Target(center_name, center_id))
              target = targets.setdefault(target_id, Target(target_name, target_id))
  
              # Link between the Target objects (see Node2)
              center + target
  
          # We take the Earth target and make it the top of the structure.
          # That way, it is easy to link it to the already declared earth-centered reference frames
          # from the `frames.frame` module.
          self.top = targets[399]